Economic and Technical Analysis of a Reverse-Osmosis Water ...

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Figure 4. RO unit with a Pelton turbine energy recovery device.2.4 Operation and maintenance of RO systemAssuming that a properly designed and constructed RO unit is installed, the major operationalelements associated with the use of this technology will be the day-to-day monitoring of thesystem and a systematic program of preventive maintenance. Operation, maintenance, andmonitoring of RO plants require trained engineering staff. Staffing levels are about one personfor a 200 m 3 /day plant, increasing to three persons for a 4,000 m 3 /day plant. Preventivemaintenance includes instrument calibration, pump adjustment, chemical-feed inspection andadjustment, leak detection and repair, and structural repair of the system on a planned schedule.The main operational concern related to the use of RO units is fouling, caused when membranepores are clogged by salts or obstructed by suspended particulates. It limits the amount of waterthat can be treated before cleaning is required. Membrane fouling can be corrected bybackwashing or cleaning (about every 4 months), and by replacement of the cartridge filterelements (about every 8 weeks). The lifetime of a membrane has been reported to be 2 to 3 years,although the literature has reported higher life spans.3. Desalination economic evaluation program (DEEP)The Desalination Economic Evaluation Program (DEEP) is a tool made freely available by theInternational Atomic Energy Agency, which can be used to evaluate performance and cost ofvarious power and water co-generation configurations [9]. The program allows designers anddecision makers to compare performance and cost estimates of various desalination and powerconfigurations. Desalination options modeled include MSF, MED, RO, and hybrid systems, andpower options include nuclear, fossil, and renewable sources. Co-generation of electricity andwater, as well as water-only plants, can be modeled. The program also enables a side-by-sidecomparison of a number of design alternatives, which helps to identify the lowest-cost optionsfor water and power production at a specific location. Data needed include the desiredconfiguration, power and water capacities, as well as values for the various basic performanceand costing data. The DEEP performance models cover both the effect of seawater salinity andtemperature on recovery ratio and required feed water pressure.The DEEP package is implemented as Excel spreadsheet files and serves three important andspecific goals:• Enables side-by-side comparison of a large number of design alternatives on a consistentbasis with common assumptions.
• Enables quick identification of the lowest-cost options for providing specified quantitiesof desalinated water and/or power at a given location.• Gives an approximate cost of desalted water and power as a function of quantity and sitespecificparameters including temperatures and salinity.4. RO system performance results and discussionA medium-size desalination RO plant with a capacity of 2,000 m 3 / day is proposed to beinstalled in Umm Qasr, a small port city in southern Iraq located on the western side of the al-Faw peninsula at 30 o 01’N latitude and 47 o 57’E longitude. DEEP-3.2 software is used for theperformance analysis of the RO system. The most important factors need to be locked at is thefresh water production cost and its quality. At normal condition, where seawater salinity isassumed to be 35,000 ppm, water feed temperature is 30 o C, and the interest rate (I.R.) is 5.0%,total water production cost is US$0.986/ m 3 , which is the total of the plant construction cost at5% I.R. (US$0.278 /m 3 ), electricity cost (US$0.178 /m 3 ), and O&M cost (US$0.530 /m 3 ). Due tothe location of the plant and the unavailable fresh water in this region, the cost is reasonable andits quality of 279 ppm is excellent, according to the price of fresh water produced by other ROplants in the world [10]. DEEP analysis results are presented in Table 1.Table 1. RO system performancePowerconsumption(kWh/m 3 )Feed flow(m 3 /day)Salinity(ppm)Fresh watercost($/m 3 )Fresh waterquality(ppm)Recoveryratio(%)Feed waterpressure(bar)Brine flow(m 3 /day)Brinesalinity(ppm)35,000 0.986 279 2.97 0.42 4,800 56.1 2,800 60,000Effect of different variables on water production costThere are many factors which has an effect on the water production cost of a desalination plant.These are: the fixed capital cost at certain interest rate which includes the building constructioncost, the equipment cost, the and installation cost; and the variable operation and maintenancecost., which include the fuel ( electricity) cost, membrane and other devices replacement cost,and the labor cost. The effects of electricity price, interest rate, feed water salinity, and feedwater temperature on the water production cost and quality were estimated using DEEP softwareand discussed below.Case 1. Effect of electricity priceBecause the high-pressure pump represents the heart of the RO unit, the cost of electricityconsumed by the pump and other electricity consuming devices in the RO plant should have asignificant effect on the water production cost. We assume in this analysis that the electricity issupplied from the grid or another central source in the region. The analysis shows that increasingthe electricity price from US$0.06 to US$0.10 per kWh will increase the cost of water by about12%. This increase seems reasonable since electricity is the only prime mover to the system.This is shown in Table 2 and presented in Figure 5.
Page 1 and 2: Economic and Technical Analysis of
Page 3 and 4: 2.1 RO system componentsThe two mos
Page 5: Materials used in SWRO modulesThe c
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